Emergency lighting refers to lighting that is activated upon power failure. An objective of emergency lighting is to allow residents in a building to leave the building safely upon power failure or in other emergency occasions. Within a building, the emergency lighting is usually provided by an emergency lighting device (e.g., LED or fluorescent lamp) powered by an emergency inverter. A battery pack is provided in the emergency lighting device.
FIG. 1 illustrates a schematic diagram of an emergency inverter 100 without a dimming function in the prior art. As illustrated in FIG. 1, in the emergency state, a lighting device driver 500 receives an output power from the emergency inverter 100 to directly drive the emergency lighting device. Because the emergency inverter 100 does not have a dimming function, the lighting device driver 500 operates in full-load in an emergency state. Further, the number of available emergency lighting devices is limited, because the total power of the emergency lighting device has to be within a rated power of the emergency inverter 100.
FIG. 2 shows a schematic diagram of an emergency inverter 200 with a preset dimming function in the prior art. As illustrated in FIG. 2, the emergency inverter 200 comprises a preset dimming unit 201 for dimming an emergency lighting device in an emergency state. When the emergency inverter 200 is applied, it is needed to calculate a dimming level based on a rated output power of the emergency inverter 200, the number of lighting device drivers 500 connected to the emergency inverter 200, and characteristics of the lighting device drivers 500. Next, the dimming level is preset by the preset dimming unit 201 so as to ensure that the total power of the emergency lighting device is kept within the rated power of the emergency inverter 200. This causes applications of the emergency inverter 200 very inconvenient. In addition, if the features or number of emergency lighting devices change, it is needed to re-calculate and preset the dimming level, which increases work load and time costs.